Numerous materials and methods have been developed for providing antimicrobial properties to medical items, consumer articles and food packaging. Nearly all of the methods thus far developed rely on the release of bacteriocides or bacteriostats to kill unwanted microbes such as bacteria, viruses, yeast, etc. There is a general problem with this approach in that the released chemicals can be harmful to the user of said items, or may leach into aquatic or surrounding environments. Materials and methods which are cleaner and safer are needed to prevent microbial contamination and infectious disease.
Small concentrations of metal-ions may play an important role in biological processes. For example, Mn, Fe, Ca, Zn, Cu and Al are essential bio-metals, and are required for most, if not all, living systems. Metal-ions play a crucial role in oxygen transport in living systems, and regulate the function of genes and replication in many cellular systems. Calcium is an important structural element in the formation of bones and other hard tissues. Mn, Cu and Fe are involved in metabolism and enzymatic processes. At high concentrations, metals may become toxic to living systems and the organism may experience disease or illness if the level cannot be controlled. As a result, the availability and concentrations of metal-ions in biological environments is a major factor in determining the abundance, growth-rate and health of plant, animal and micro-organism populations.
It has been recognized that iron is an essential biological element, and that all living organisms require iron for survival and replication. Although the occurrence and concentration of iron is relatively high on the earth's surface, the availability of “free” iron is severely limited by the extreme insolubility of iron in aqueous environments. As a result, many organisms have developed complex methods of procuring “free” iron for survival and replication. Controlling the concentration of “free” iron in any biological system can, therefore, allow one to control the growth rates and abundance of micro-organisms. Such control can be of great use for treating sickness and disease, inhibiting bacterial growth, treating wounds, and providing for the general health of plant, animal, micro-organism and human populations. Indeed, iron “chelating” or “sequestering” drugs are used to treat iron deficiency in plants; and are used to treat diseases such as Cooley's anemia (thalassemia), sickle-cell anemia, and iron overload diseases in humans.
Metal-ions may also exist as contaminants in environments such as drinking water, beverages, food, industrial effluents and public waste waters, and radioactive waste. Methods and materials for removing such contaminants are important for cleaning the environment(s) and providing for the safety of the general public.
U.S. Pat. No. 5,217,998 to Hedlund et al. describes a method for scavenging free iron or aluminum in fluids such as physiological fluids by providing in such fluids a soluble polymer substrate having a chelator immobilized thereon. A composition is described which comprises a water-soluble conjugate comprising a pharmaceutically acceptable water-soluble polysaccharide covalently bonded to deferoxamine, a known iron chelator. The conjugate is said to be capable of reducing iron concentrations in body fluids in vivo.
U.S. Pat. No. 6,156,334 to Meyer-Ingold et al. describes novel wound coverings which can remove interfering factors (such as iron ions) from the wound fluid of chronic wounds. The wound coverings may comprise iron chelators covalently bonded to a substrate such as cloth or cotton bandages. U.S. patent application US 2003/0078209 A1 to Schmidt et al. describes solid porous compositions, substantially insoluble in water, comprising at least 25% by weight of an oxidized cellulose and having a significant capacity to bind iron. The invention also provides a method of sequestering dissolved iron from aqueous environments. The compositions may be used for the prevention or treatment of infections by bacteria or yeast.
U.S. Pat. No. 6,489,499 B1 to King et al. describes novel compounds comprising siloxane modified carboxylic acid substituted amines. The compounds of the invention are said to provide many of the desirable properties of ethylene diammine tetraacetic acid and its salts in a stationary phase. The stationary substrate may comprise silicate glass, silica, alumina, inorganic clays, etc. Markowitz et al. (J. Phys. Chem. B. 104, 10820 (2000)) describes metal chelating agents, such as carboxylic acid substituted amines, covalently bound to mesoporous silica. Tien (Chem. Mater. 11, 2141(1999)) describes silica gels functionalized with carboxylic acid substituted amines, the functionalization of which was accomplished using siloxane modified carboxylic acid substituted amines. The usefulness of the material “as a stationary phase for chromatographic separation of metal-ions” was demonstrated.
The materials and methods described above, while capable of sequestering metal-ions, are limited in their capacity for several reasons. First, because the particle size of the substrate or of the stationary phase is large (>1 micron), only a limited amount of metal-ion sequestering agent can be applied to the surfaces of the substrate. This is especially true if the substrate or stationary phase contains no internal surfaces (i.e., are not porous). Metal-ion sequestering agent in excess of the available surface area, cannot be bound to the substrates surfaces, and therefore, will not be effective in sequestering or separating metal-ions from the contacting environment. Because sequestering media prepared as in the prior art have limited capacity, large amounts of material are required to effectively remove metal-ions and their application can be costly. Additionally large particles strongly scatter light, and cannot be applied to transparent or colored surfaces or articles without rendering the surface or article opaque or white. This alters significantly the appearance of the article containing the sequestering agent and precludes the use of large particles in many applications.
Materials are needed that are able to target and remove specific metal-ions, while leaving intact the concentrations of beneficial metal-ions. Furthermore, materials are needed that have a high capacity for metal-ions and that provide for the efficient removal of metal-ions in a cost effective manner. Materials and methods are needed for sequestering metal-ions even in extremely low concentrations and removing metal-ion contaminants to levels below 100 parts per billion (ppb) and still further below 10 ppb. Materials and methods are needed for applying immobilized metal-ion sequestraints to numerous items and articles without significantly changing their color or appearance.